The fluid conduit elements, typically, have a conduit part with a cylindrical connection end made of metal. The conduction element further has a flexible bellows, which can be made of ring-shaped corrugations or screw-like spiral corrugations. Within the flexible bellows, coaxially arranged, is a woven or knitted hose made of metal wire. The conduit as well as the hose are securely connected at a common end. The outer diameter of the hose essentially corresponds to the clear inner diameter of the conduit element. At a further location in the longitudinal extent of the hose, the wires are irremovably relatively positioned with respect to each other around the circumference of the hose.
Conduit elements which have bellows are often also simply referred to as flexible corrugated hoses. They are made directly from a pipe to be absolutely tight, or practically tight, by spiral winding of a pre-profiled metal ribbon or tape. The conduit elements of this absolutely or practically fluid-tight connection, between two spaced pipes or other conduits, form, in a preferred case, a flexible connection within the entire exhaust gas system of an internal combustion engine, e.g. in an automotive vehicle. The flexible conduit element is provided in order to permit motion to occur, particularly engine oscillations and vibrations, without transfer of such vibrations or motions to the frame of the vehicle, and hence to the passenger compartment thereof. Preferably, these fluid conduit elements are absolutely fluid-tight, especially gas-tight.
The bellows portion itself of the fluid conduit, in dependence on required flexibility, can be made as a single-wall or multiple-wall structure. If a multiple-wall structure is used, the separate layers of the wall may be made of different materials, especially in view of corrosion effects which might differentially affect different materials. The cross-sectional shape need not be circular, but may be oval, which is used sometimes to properly fit the conduit element within available space.
The interior hose within the conduit element, fixed at one end, is used to guide the exhaust stream within the bellows and thus avoids turbulences or eddies at the inner protrusions of the corrugations of the bellows, and thereby decreases flow noises and secondary noise generation. Additionally, the inner protrusions of the corrugations of the bellows are then thermally less stressed, which also increases the lifetime of the bellows portion of the fluid conduit element.
Structures of this type in accordance with the prior art have seated the inner hose loosely or limp within the fluid conduit, except at the point of its attachment at one end to the fluid conduit element. The hose, thus, cannot accept any tasks other than those previously mentioned. Especially, it is not possible to use the hose to directly influence oscillations or vibrations of the bellows, and hence of the conduit element itself which may transfer vibrations and oscillations between connected other conduits or pipes. The interior hose likewise cannot affect the behavior of the bellows or of the conduction element as a whole with respect to resonance. Oscillations and vibrations always have accompanying acoustic effects which are annoying to persons within the vehicle.